It's implied in the article that 300,000 lines of code is the total written by the company (of which the author is a founder), not by the individual author. With a company that's 3 years old, 41 man-years implies a staff of roughly 15-20, which is quite reasonable for a startup.
And written for "hundreds" of clients according to the author, which basically implies a good chunk of the 300k lines to be duplicates, with a relative ammount of customization.
That sounds reasonable for application code. 15-20 People working on architecture code for 3 years? That sounds like an unreasonable amount of developers dedicated to devops for a startup
